Security element formed from at least two inks applied in overlapping patterns, articles carrying the security element, and authentication methods

Abstract

Security element including a first and second pattern formed by a first and second material respectively in or on a first and a second region of a substrate respectively, the first pattern partially overlapping with said second pattern, the first material comprising a first luminescent dye, which upon excitation by electromagnetic radiation falling within its excitation wavelength range emits electromagnetic radiation in a first emission wavelength range, the second material comprising a second luminescent dye, which upon excitation by electromagnetic radiation falling within its excitation wavelength range emits electromagnetic radiation in a second emission wavelength range, said first emission wavelength range overlapping with the excitation wavelength range of the second luminescent dye, so that upon irradiation within the excitation wavelength range of the first luminescent dye the second luminescent dye is excited, in the overlapping area of the patterns, to emit electromagnetic radiation in the emission wavelength range.

Description

[0001]The present invention concerns a security element comprising at least two patterns PAT1 and PAT2 formed from two inks INK1 and INK2, respectively. Each of INK1 and INK2 comprises a luminescent (i.e. fluorescent and / or phosphorescent) dye or pigment, whereof the one present in INK1 (“the donor”) is capable of exciting the other present in INK2 (“the acceptor”), resulting in a cascade effect in terms of energy transfer in overlapping areas of PAT1 and PAT2. The present invention also relates to the use of this security element for authenticating articles, such as banknotes, value papers, identity documents, cards, tickets, labels, security foils, security threads and the like, articles being provided with the security element, and a method for the authentication of such articles.1. BACKGROUND ART[0002]The authentication of luminescent, in particular fluorescent, markers with imaging devices is commonly accomplished by imaging / observing the authentication mark in a certain spectr...

AI Technical Summary

Benefits of technology

The cascade effect provides a robust and reliable authentication method that is simpler to implement, resistant to counterfeiting, and can be used in handheld devices without the need for complex equipment, ensuring the security element's genuineness.

Problems solved by technology

This approach has the drawback that the emission spectra of common markers (e.g. fluorescent dyes and pigments) can either be known in advance or can be easily determined.

Therefore, in terms of authentication, this method cannot be considered as reliable, since other marking dyes emitting in a close range may provide enough contrast to be considered as genuine.

With a standard imaging sensor, performing multi (or hyper) spectral imaging, e.g. in the NIR (near infrared range) range, would require techniques such as: (1) custom Bayer-like filters (involving expensive developments) (2) Fabry-Perot configurations (currently bulky and fairly expensive), (3) complex cameras using AOTF (Acousto-Optic Tunable Filters, which also bulky and expensive), (4) switchable band-pass interference filters (with inconvenient moving parts), or (5) imaging spectrographs requiring push-brooms (unsuitable for handheld readers).

Thus, the finer analysis of spectral properties generally requires complex, bulky and expensive equipment, and is difficult to implement in handheld devices or widely distributed authentication equipment.

However, this device does not provide an image of the mark, making it unsuitable for code reading or geometrical checks of the printed mark.

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